The invention relates to a progressive sequence for producing a selected portion of a formation containing viscous oil. More particularly, wells in a series of patterns progressively extending across a segment of a formation are subjected to a combination of electrical heating with brine injection, hot water inject and production.
In the recovery of oil from viscous oil bearing formations it is usually possible to produce only a very small portion of the original in-place oil by natural or primary production which relies solely on the natural forces present in the formation. A variety of artificial recovery techniques, therefore, have been employed to increase oil recovery. The most commonly applied technique is water flooding in which water is injected at a pressure sufficient to displace oil in the reservoir toward producing wells. Water flooding has little success in displacing viscous oil which is essentially in its viscous natural state. Steam injection has been used, but steam displacement uses heat inefficiently and its use is limited. Steam soaks and huff and puff techniques have been used with and without foaming, surfactant and caustic agents, but by themselves these techniques have limited application. More recently, it has been proposed, for example, in U.S. Pat. Nos., 3,642,066; 3,874,450, 3,848,671, 3,948,319; 3,958,636; 4,010,799 and 4,084,637, to use electrical current to add heat to a subsurface pay zone containing tar sands or viscous oil to render the viscous hydrocarbons more flowable. In general, two or more electrodes are connected to an electrical power source and are positioned at spaced apart points in contact with the earth in a manner such that when electric current is passed between the electrode it will heat viscous oil in a subsurface formation. Voltages of a couple of hundred volts and up to and exceeding 1000 volts are applied to the electrodes. Currents up to 1800 amperes are passed between the electrodes. Electrical heating processes are consistent with creating temperatures that cause the most benefit, but most of the heat occurs adjacent to the electrode and heat transfer outward into the formation by conduction is slow. Moreover, the power efficiency of electrical generation is only about one-third. Brine and factures have been used to decrease electrode resistance and increase electrode radius. Moreover, it has been proposed to use the electrode wells and aqueous injection wells in well patterns based in part on the number of phases of the electricity used to apply heat to the formation. Such patterns have been used in conventional ways and their efficiency, therefore, is less than it could be.
It is the primary object of this invention to provide an electric heating, injection and production sequence that progressively produces a selected portion of a viscous oil bearing formation in an efficient and more complete manner.